Fabrics, by virtue of their construction, the material of which their fibres or threads are made, or their finish, have different degrees of resistance to penetration by a sewing needle. Knitted fabrics, of which increasing use is being made, are particularly prone to sewing defects caused by needle damage (see "Sewability of Knitted Fabrics" by Carol A. Leeming and D. L. Munden, Clothing Research Journal Vol. 1 No. 2 1973, The Clothing Institute, London). It sometimes happens that a batch of fabric is especially difficult to sew, which results in considerable wastage through faulty sewing, or possibly an expensive re-processing of the fabric. Testing the fabric before purchase, or, by the fabric producer during production, can avoid expensive mistakes.